The invention relates to alignment of an interferometer module for use in an exposure tool. Exposure tools comprising an optical column and a target carrier for carrying a target to be exposed and for moving said target relative to said optical column, often comprise an interferometer for accurately determining the position of the target within the exposure tool. In order to work properly, such an interferometer must be aligned with other parts of the exposure tool, e.g. with a mirror on said target carrier and/or a mirror on said optical column. When replacing the interferometer, for instance for performing maintenance thereon or for upgrading the tool, the replacement interferometer must be aligned relative to said exposure tool, in particular relative to the mirrors in the tool onto which the interferometer emits its beams. The time required for such an alignment procedure increases the downtime of the exposure tool when replacing an interferometer.
It is an object of the invention to provide an interferometer module, method and exposure tool for reducing downtime during replacement of the interferometer in the exposure tool.